The invention relates to an apparatus for treating skins or hides with liquids in so-called wet processes, e.g. liming, drenching, tanning, dyeing or the like, comprising a liquid-impermeable substrate inflexibly receiving the hide and a treatment device substantially tightly applicable to the top of the hIde by means of which the treatment liquid penetrates the skin under high pressure.
In leather processing the term wet processes is used for the treatment stages in which the skin or hide is treated with dissolved chemicals and where there is a high liquid requirement This includes the soaking of the skin, liming in a strong alkaline solution, deliming (neutralizing) in an acid solution, drenching, e.g. by means of proteolytic enzymes, pickling by means of acids and salts, tanning, e.g. by means of chromium-lII-salts, retanning and dubbing the hide, as well as dyeing. Most of these wet processes in conventional tanneries take place in vat-like containers, accompanied by multiple circulation and for varyingly long action times, large liquid quantities being required and are constantly circulated.
These tannery wet processes are technically unsatisfactory for several reasons. The hide must pass through a plurality of process stages, which in part take place batchwise with a hide weight of up to 20 tons, but in part in individual form. This requires several times the dividing up of the batches, individualizing and orientation of the hides, e g. alignment or orientation on the basis of the head and butt, which is correspondingly time and labour-consuming. Large hides or skins can have a surface area up to 6 m.sup.2 and can weigh up to 100 kg, as a function of the water content. As transportation must take place manually over considerable distances within the tannery, a correspondingly large labour requirement exists. As a result of the corrosive chemicals and the organic substance emanating from the hide, it is scarcely possible to bringabout hygienic working conditions for personnel. There is in particular the problem of getting rid of large waste water quantities, particularly as the treatment liquids can only be reused to a very limited extent.
Dyeing processes have been improved somewhat (German patent 822 060), in that the hides are placed on a belt and led part a dye spraying device, which makes it possible to at least reduce the difficulties during the handling of the hide. However, here again, the need for dyeing liquid is considerable, because it is sprayed at a distance onto the hide, so that a large amount of dyeing liquid does not reach the hide and consequently a considerable action time is required to ensure that the dyeing liquid penetrates the hide. In this way, thorough dyeing is either impossible, or requires a considerable amount of time. In the other aforementioned wet processes, the treatment liquid must intensely and completely penetrate the hide, so that it must be in constant contact with the treatment liquid for a long time. In order that in said wet processes it is possible to have a planned working with minimum liquid requirement, it has been proposed (EP-OS 0 009 081), to introduce the treatment liquid into the skin under high pressure in the manner of an injection process.
In this injection process it is possible to work with highly concentrated treatment liquids, so that the water requirement is much lower than in conventional tannery processes. Only a comparatively small treatment liquid excess has to be used, which must merely ensure that the entire thickness of the hide is penetrated by the treatment liquid. This process is carried out by means of injection nozzles similar to injection guns, which can be placed on the hide and by means of which the treatment liquid can be forced under a high pressure of more than 50 bar into the hide. Within the actual hide, the treatment liquid is spread out in roughly circular manner over a somewhat larger area. In order to treat a hide in this way, a large number of such injection nozzles is required. Tests over many years with this process have not led to satisfactory results. There are many reasons for this. Thus, difficulties are encountered in injecting the treatment liquid in uniform manner over the entire skin surface and cross-section. Thus, besides thoroughly tanned areas, there are inadequately tanned areas. The different thickness of the hide also leads to problems. The treatment liquid pressure level must be designed for the greatest hide thicknesses, i.e. for example in the neck and back regions, so that in the thin skin regions the treatment liquid is shot through the skin and cannot therefore have its desired action. Finally, skin damage can occur as a result of the high pressures, particularly in the vicinity of the injection nozzle attachment. Thus, this process only permits a waste-free operation from the flesh side of the hide. However, even here the hide must be left for a certain time to enable the treatment liquid forced in in jet-like manner to completely penetrate. This lateral penetration then varies very considerably as a function of the hide thickness.
It is finally impossible with acceptable equipment and general costs to treat a complete hide in a single operation. Thus, in the aforementioned apparatus (EP-OS 0 009 081), the hide is moved in synchronized manner passed two successively arranged and reciprocally displaced nozzle rows, so that it is only zonally treated. The injection pressure is absorbed by the inflexible support, which presses -he hide against the injection nozzles.
The problem of the present invention is to so improve the aforementioned apparatus that, with reduced operating pressure, a uniform penetration of the treatment liquids into the skin or hide is ensured.
According to the invention this problem is solved in that the treatment device has several liquid supply ducts arranged approximately perpendicular to the substrate and which on the underside of the device facing the hide are widened in large-area manner and are arranged in surface-filling manner thereon and that between the underside of the device and the hide is provided a net-like support and the gap between the substrate, hide, support and treatment device is substantially tightly sealable with respect to the outside. In the inventive apparatus, in the vicinity of their opening, the supply ducts have a comparatively large-area extended or widened portion of e.g. several cm.sup.2, said widened portions having a geometrical contour and an arrangement such that they are closely linked with one another and cover a large-surface area. In order that the treatment liquid entering the widened portions through the supply ducts is injected into the skin in uniform manner over the widened portion cross-section, the net-like support is provided on the hide, which on the one hand levels the hide somewhat in said area and on the other ensures a punctiform penetration of the treatment liquid over a large cross-section. In order to avoid a pressure drop to the outside the gap provided between the substrate, the hide, the support and the treatment device is tightly sealable to the outside. This is generally made possible in that the parts are moved correspondingly tight together, without separate edge-side seals being required.
Practical tests with the aforementioned apparatus have revealed a number of advantages. Thus, it is possible to work with much lower pressures than proposed by the prior art. An adequate, large-area penetration is ensured at a pressure of about 10 bar. As a result and through the large-area action, skin or hide damage is completely prevented. As a function of the nature of the wet process, the treatment liquids can be injected from the flesh or grain side. The treatment device can also have a large area, so that a complete hide can be treated in a single operation, so that the action time and overall treatment period can be considerably reduced. Due to the large-area action of the treatment liquid and the lower operating pressure, it is ensured that the treatment liquid effectively penetrates independently of the hide thickness and is distributed throughout the hide. "Shooting through" cannot occur, particularly in thin hide areas. This is also aided by the fact that, unlike in high pressure injection nozzles, the low pressure of approximately 10 bar can be maintained for a longer period in the widened portions and therefore on the hide
The large-area widened portions of the supply ducts on the underside of the treatment device can have a polygonal or circular contour, in whose centre issues at least one supply duct in each case. The widened portions can e.g. have a contour in the form of equilateral triangles, squares, polygons or circles.
As is known per se, also in the case of the inventive apparatus it is possible to provide a net-like intermediate layer between the hide and the substrate, to permit the draining off of the treatment liquids penetrating the hide. However, as such an intermediate layer would be too flexible in order to receive and withstand the treatment pressure at the other side, it is also necessary to provide an inflexible substrate, which then has several juxtaposed drains for the treatment liquid penetrating the skin. The excess treatment liquid penetrating the skin or hide consequently passes through the fine-mesh intermediate layer to the inflexible substrate, where it is led away through the drains.
In a preferred embodiment of the invention the net-like support and intermediate layer are formed by a fine-mesh plastic or metal net, which on the one hand has the necessary flexibility for adapting to unevenesses of the hide and on the other hand has the necessary strength to resist the operating pressure, without the mesh width changing under the action of the operating pressure. It is admittedly known (German patent 822 060) to use metal nets as a substrate for hides, in order to permit a draining of the treatment liquid (dyeing liquid), whilst it is also known to use such metal nets during the pressing of water out of the hides. However, in the present invention the metal net fulfils another function, namely in that it forms a support for the hide, which uniformly distributes the treatment liquid supplied from the outside and allows it to penetrate the hide in punctiform manner.
According to another embodiment the underside of the treatment device or the widened or extended portions arranged there in surface-filling manner can, in one extension direction, have an extension corresponding to the hide width or length. In this case the treatment liquids are injected stripwise into the skin, which is in turn moved intermittently through the apparatus.
However, according to a preferred embodiment, the underside of the treatment device or the extended portions of the supply ducts arranged there in surface-filling manner cover a surface roughly corresponding to the surface of a hide. This embodiment makes it possible to treat a complete hide in one operation, so that a high throughput can be achieved.
According to another embodiment the support and intermediate layer receiving the hide between them are constructed as conveyor belts. Thus, the hide can be placed between the two conveyor belts and conveyed between them into the apparatus, so that the necessary manual activities for the complete treatment are restricted to placing the hide on the entry to the conveyor belts and removing the hide at the exit therefrom. Optionally the hide can be ejected at the exit from the conveyor belts.
According to another development of the invention the substrate is constructed as a table and can be raised against the treatment device. In this case the skin is introduced by means of the metal nets constructed as conveyor belts between the substrate and the treatment device, the table is then raised against the latter, accompanied by the simultaneous pressing of intermediate layer, hide and support against the treatment device and accompanied by tight sealing against the outside, after which the treatment liquid can be supplied by means of the supply ducts.
Another embodiment is inventively characterized in that the substrate is constructed as a revolving link belt, between whose links the treatment liquid can drain off. In this case the link belt forms an adequately inflexible support for the hide, which is here again conveyed between the fine-mesh intermediate layer and a support.
In this embodiment, the link belt can be guided in trough-like manner in the vicinity of the treatment device and the underside of the latter can be curved so as to fill the trough. In this embodiment the hide is conveyed between the support and the intermediate layer into the trough between the treatment device and the link belt and can be treated intermittently, or advantageously continuously.
In the case of a continuous treatment, it is appropriate if the treatment device is constructed as a revolving cylinder, on whose circumference are arranged the widened portions of the supply ducts, which are controllable in their opening position only in the vicinity of the trough. In this embodiment with a treatment device concomitantly rotating with the link belt, there is no relative movement between the hide and the treatment device, i.e. despite the continuous operation, it is ensured that the widened portions on the underside of the treatment device always remain in the same relative position with respect to the hide, so that the action time of the treatment liquid is exclusively controllable by the conveying speed through the trough gap. In this way, movement through the treatment device can take place with juxtaposed hides.
According to another development of the invention with the fine-mesh support and intermediate layer is associated outside the treatment device at least one cleaning device, e.g. a spraying device, by means of which it is possible to eliminate any contaminants or dirt which has deposited between the meshes and which come from the skin. The spraying device can be operated with compressed water or air. This ensures that in particular the fine-mesh support has free mesh cross-sections prior to each entry into the apparatus, so as to permit a completely satisfactory distribution of the treatment liquids.
The inventive apparatus is also characterized by a collecting container penetrating the hide and receiving excess treatment liquid and from which the latter can be recirculated. As the inventive apparatus gives the possibility to work with highly concentrated treatment liquids and during the actual treatment said liquids undergo no or only minimum changes to their composition, the excess treatment liquid can be reused. Optionally a purely mechanical treatment, e.g. the filtering of the treatment liquid is sufficient, to enable it to be resupplied to the treatment device. It is only necessary to quantitatively compensate the losses resulting from the penetration of the hide, Large waste water quantities are not produced, because it is only necessary to eliminate that treatment liquid, which can no longer be reused for chemical and/or physical reasons. This is constituted by extremely small quantities with known constituents, which can easily be dealt with by the waste disposal system.
According to another advantageous development with the treatment device is associated a large-volume pressure vessel for the treatment liquids, which on the one hand is provided with the collecting container and on the other with a feedline for the fresh treatment liquid. By means of the pressure vessel, e.g. an air chamber, an identical pressure can be maintained in easy manner for all the supply ducts. The pressure vessel is on the one hand supplied from the collecting container with the recirculated treatment liquid and on the other hand, for compensating the liquid remaining in the skin and any other liquid which may be lost, with fresh treatment liquid. Instead the treatment device can be directly supplied by pumps.
It is finally appropriate if chemical-physical sensors are arranged in the collecting container or pressure vessel enabling the feedline to be controlled for fresh treatment liquid in order to maintain given concentrations in the pressure vessel. This makes it possible to achieve a completely automated sequence of wet processes in the tannery.